Question

Calculate the pH of solutions with a [H+] of 6.4 x 10-12M

Calculate the [H+] and [HO-] for a pH 7.4 solution:

[H+] =

[HO-] =

3. What is the pH of a 0.3M solution of acetic acid? (the pKa for acetic acid is 4.75)

4. Sketch a drawing or use Excel or other graphing software to draw a titration curve for histidine. Label the graph with pI, pKa, and equivalence point.

Would phenylalanine be a good physiologic buffer? Why?

Would any of the 20 amino acids be good physiologic buffers? Why?

7. What is the percentage of tryptophan with protonated amino groups at pH 7.4?

Answer 1

1) Calculate the pH of solutions with a [H+] of 6.4 x 10-12M

[H+] = 6.4 x 10^-12 M

pH = -log [H+]

pH = - log (6.4 x 10^-12)

pH = 11.2

2) Calculate the [H+] and [HO-] for a pH 7.4 solution:

[H+] = 10^-7.4

[H+] = 3.98 x 10^-8 M

[HO-] = Kw / [H+]

          = 1.0 x 10^-14 / (3.92 x 10^-8)

[HO-]   = 2.51 x 10^-7 M

3.) What is the pH of a 0.3M solution of acetic acid? (the pKa for acetic acid is 4.75)

pH = 1/2 [pKa - log C]

pH = 1/2 [4.75 - log 0.30]

pH = 2.64